The man who drove a car through a perimeter fence at BWI Thurgood Marshall Airport on Saturday afternoon made it onto an airplane with a backpack before authorities could catch up to him and detain him, Maryland Transportation Authority Police confirmed Monday.

"Yes, he did enter an unoccupied aircraft," said Lt. Kevin Ayd, a MdTA Police spokesman. "The aircraft and the backpack were checked, and there was nothing that was alarming."

The backpack contained only "papers and personal effects," and the FBI determined "this was not terrorism-related," Ayd said.

The FBI confirmed it does not believe there is a terrorism link, and added that they were assisting MdTA with their investigation and are not the lead agency.

Police had reported the breach of the perimeter fence on Saturday, but not the fact that the man had boarded a plane.

Ayd said the plane was a smaller-model aircraft, such as those that are boarded not directly from terminal gates but via stairs on the tarmac. He said he did not know who owned the aircraft, or whether the owner was a major airline.

Ayd said the man drove his car through the perimeter fence near Signature Flight Support off Aviation Boulevard about 1:30 p.m. Saturday.

An investigation showed the man — identified as a 42-year-old from Laurel — had entered the plane at Pier D near the terminal with the backpack, left the backpack on board, left the plane, and then gone back into the plane before police arrived, Ayd said.

The man remained in a local hospital under "evaluation" on Monday, Ayd said. He would not elaborate on what sort of evaluation it was.

Police named the man, but The Baltimore Sun is not identifying him because he has not been charged with a crime. MdTA Police are the lead investigating agency, but would be determining charges in conjunction with the FBI, Ayd said.

Ayd said security is the MdTA's "No. 1 priority," and the agency "will review the incident and see what steps need to be taken" to make sure similar incidents don't occur in the future.

Jonathan Dean, a spokesman for BWI, said the incident was a "law enforcement matter" that he could not comment on.

"The airport will review this matter with relevant security and law enforcement agencies," he said.